TOCHI 1996 Volume 3 Issue 1

Norman proposed a model describing the sequence of user activities involved
in human-computer interaction. Through this model, Norman provides a rationale
for why direct-manipulation interfaces may be preferred to other design
alternatives. Based on action identification theory we developed several
hypotheses about the operations of Norman's model and tested them in a
laboratory experiment. The results show that users of a direct-manipulation
interface and a menu-based interface did not differ in the total amount of time
used to perform a task. However, with the direct-manipulation interface, more
time is devoted to performing motor actions, but this is offset by shorter
nonmotor time. Furthermore, there are significant interactions between task
familiarity, instructions, and the type of interface, indicating that Norman's
model may not hold under all conditions.

We conducted a study to investigate the use of generic versus task-specific
application software by people who create and maintain presentation slides.
Sixteen people were interviewed to determine how they prepare slides, what
software they use to prepare and maintain slides, and how well the software
they use supports various aspects of the task. The informants varied in how
central slidemaking was to their jobs. The hypotheses driving the study were
that: (1) some software applications are task generic, intended for use in a
wide variety of tasks, while others are task specific, intended to support very
specific tasks; (2) task-specific software is preferable, but is often not used
because of cost, learning effort, or lack of availability, and (3) people who
infrequently perform a task tend to use generic tools, while people who often
perform it tend to use task-specific tools. Our findings suggest that several
factors influence choice of slidemaking software, including desired quality,
production time, user skill, willingness to use multiple tools, whether people
work alone or in teams, and company policy. Furthermore, the task
specificity/genericness of an application program is not a simple matter of
degree, because it depends on several fairly independent software design
issues. We (1) conclude that developing application software that supports all
aspects of a task well is extremely difficult and (2) suggest an alternative
approach that may be more fruitful: providing collections of interoperable
tools and services.

This article presents an overview of GroupKit, a groupware toolkit that lets
developers build applications for synchronous and distributed computer-based
conferencing. GroupKit was constructed from our belief that programming
groupware should be only slightly harder than building functionally similar
single-user systems. We have been able to significantly reduce the
implementation complexity of groupware through the key features that comprise
GroupKit. A runtime infrastructure automatically manages the creation,
interconnection, and communications of the distributed processes that comprise
conference sessions. A set of groupware programming abstractions allows
developers to control the behavior of distributed processes, to take action on
state changes, and to share relevant data. Groupware widgets let interface
features of value to conference participants to be easily added to groupware
applications. Session managers -- interfaces that let people create and manage
their meetings -- are decoupled from groupware applications and are built by
developers to accommodate the group's working style. Example GroupKit
applications in a variety of domains have been implemented with only modest
effort.

TOCHI 1996 Volume 3 Issue 2

A new method is presented for performing rapid and accurate numerical
estimation. The method is derived from an area of human cognitive psychology
called preattentive processing. Preattentive processing refers to an initial
organization of the visual field based on cognitive operations believed to be
rapid, automatic, and spatially parallel. Examples of visual features that can
be detected in this way include hue, intensity, orientation, size, and motion.
We believe that studies from preattentive vision should be used to assist in
the design of visualization tools, especially those for which high-speed target
detection, boundary identification, and region detection are important. In our
present study, we investigated two known preattentive features (hue and
orientation) in the context of a new task (numerical estimation) in order to
see whether preattentive estimation was possible. Our experiments tested
displays that were designed to visualize data from salmon migration
simulations. The results showed that rapid and accurate estimation was indeed
possible using either hue or orientation. Furthermore, random variation in one
of these features resulted in no interference when subjects estimated the
percentage of the other. To test the generality of our results, we varied two
important display parameters -- display duration and feature difference -- and
found boundary conditions for each. Implications of our results for
application to real-world data and tasks are discussed.

A user interface study concerning the usage effectiveness of selected
retrieval modes was conducted using an experimental text retrieval system,
TeSS, giving access to online documentation of certain programming tools. Four
modes of TeSS were compared: (1) browsing, (2) conventional boolean retrieval,
(3) boolean retrieval based on Venn diagrams, and (4) these three combined.
Further, the modes of TeSS were compared to the use of printed manuals. The
subjects observed were 87 computing new to them. In the experiment the use of
printed manuals is faster and provides answers of higher quality than any of
the electronic modes. Therefore, claims about the effectiveness of
computer-based text retrieval have to by vary in situations where printed
manuals are manageable to the user. Among the modes of TeSS, browsing is the
fastest and the one causing the fewest operational errors. On the same two
variables, time and operational errors, the Venn diagram mode performs better
than conventional boolean retrieval. The combined mode scores worst on the
objective performance measures; nonetheless nearly all subject prefer this
mode. Concerning the interaction process, the subjects tend to manage the
complexities of the information retrieval tasks by issuing series of simple
commands and exploiting the interactive capabilities of TeSS. To characterize
the dynamics of the interaction process two concepts are introduced; threads
and sequences of tactics. Threads in a query sequence describes the continuity
during retrieval. Sequences of tactics concern the combined mode and describe
how different retrieval modes succeed each other as the retrieval process
evolves.

Many information structures are represented as two-dimensional networks
(connected graphs) of links and nodes. Because these network tend to be large
and quite complex, people often prefer to view part or all of the network at
varying levels of detail. Hierarchical clustering provides a framework for
viewing the network at different levels of detail by superimposing a hierarchy
on it. Nodes are grouped into clusters, and clusters are themselves place into
other clusters. Users can then navigate these clusters until an appropriate
level of detail is reached. This article describes an experiment comparing two
methods for viewing hierarchically clustered networks. Traditional full-zoom
techniques provide details of only the current level of the hierarchy. In
contrast, fisheye views, generated by the "variable-zoom" algorithm described
in this article, provide information about higher levels as well. Subjects
using both viewing methods were given problem-solving tasks requiring them to
navigate a network, in this case, a simulated telephone system, and to reroute
links in it. Results suggest that the greater context provided by fisheye
views significantly improved user performance. Users were quicker to complete
their task and made fewer unnecessary navigational steps through the hierarchy.
This validation of fisheye views in important for designers of interfaces to
complicated monitoring systems, such as control rooms for supervisory control
and data acquisition systems, where efficient human performance is often
critical. However, control room operators remained concerned about the size
and visibility tradeoffs between the fine room operators remained concerned
about the size and visibility tradeoffs between the fine detail provided by
full-zoom techniques and the global context supplied by fisheye views.
Specific interface features are required to reconcile the differences.

TOCHI 1996 Volume 3 Issue 3

It has suggested that interactive computer users find "exploratory learning"
to be an effective and attractive strategy for learning a new system or
investigating unknown features of familiar software. In exploratory learning,
instead of working through precisely sequenced training materials, the user
investigates a system on his or her own initiative, often in pursuit of a real
or artificial task. The value of exploratory learning has been studied in
controlled settings, with special attention newly acquired systems, be there
has been little investigation of its occurrence in natural situations or in
support of ongoing learning. To address this question, a field study of the
behavior and attitudes of computer users in everyday working situations was
performed, using diaries and structured interviews that focused on learning
events. The study showed that task-oriented exploration was a widely accepted
method for learning, but that it often required support from manuals and from
other users or system support personnel. Exploration not related to a current
or pending task was infrequent, and most users believed it to be inefficient.
These findings have implications for the design of systems, documentation, and
training.

Software reuse, a long-standing and refractory issue in software technology,
has been specifically emphasized as an advantage of the object-oriented
programming paradigm. We report an empirical study of expert Smalltalk
programmers reusing user interface classes in small graphical applications.
Our primary goal was to develop a qualitative characterization of expert reuse
strategies that could be used to identify requirements for teaching and
supporting reuse programming. A secondary interest was to demonstrate to these
experts the Reuse View Matcher -- a prototype reuse tool -- and to collect some
initial observations of this tool in use during reuse programming. We observed
extensive "reuse of uses" in the programmers' work: they relied heavily on code
in example applications that provided an implicit specification for reuse of
the target class. We called this implicit specification a "usage context." The
programmers searched for relevant usage contexts early. They repeatedly
evaluated the contextualized information to develop solution plans, and they
borrowed and adapted it when the sample context suited their immediate reuse
goals. The process of code development was highly dynamic and incremental;
analysis and implementation were tightly interleaved, frequently driven by
testing and debugging. These results are considered in terms of the tradeoffs
that inhere in the reuse of uses and the teaching and tool support that might
improve the efficiency and accuracy of this approach to reuse.

This study investigates human performance when using semitransparent tools
in interactive 3D computer graphics environments. The article briefly reviews
techniques for presenting depth information and examples of applying
semitransparency in computer interface design. We hypothesize that when the
user moves a semitransparent surface in a 3D environment, the
"partial-occlusion" effect introduced through semitransparency acts as an
effective cue in target localization -- an essential component in many 3D
interaction tasks. This hypothesis was tested in an experiment in which
subjects were asked to capture dynamic targets (virtual fish) with two versions
of a 3D box cursor, one with and one without semitransparent surfaces. Results
showed that the partial-occlusion effect through semitransparency significantly
improved users' performance in terms of trial completion time, error rate, and
error magnitude in both monoscopic and stereoscopic displays. Subjective
evaluations supported the conclusions drawn from performance measures. The
experimental results and their implications are discussed, with emphasis on the
relative, discrete nature of the partial-occlusion effect and on interactions
between different depth cues. The article concludes with proposals of a few
future research issues and applications of semitransparency in human-computer
interaction.

TOCHI 1996 Volume 3 Issue 4

Since the seminal book, The Psychology of Human-Computer Interaction, the
GOMS model has been one of the few widely known theoretical concepts in
human-computer interaction. This concept has spawned much research to verify
and extend the original work and has been used in real-world design and
evaluation situations. This article synthesizes the previous work on GOMS to
provide an integrated view of GOMS models and how they can be used in design.
We briefly describe the major variants of GOMS that have matured sufficiently
to be used in actual design. We then provide guidance to practitioners about
which GOMS variant to use for different design situations. Finally, we present
examples of the application of GOMS to practical design problems and then
summarize the lessons learned.

Since the publication of The Psychology of Human-Computer Interaction, the
GOMS model has been one of the most widely known theoretical concepts in HCI.
This concept has produced several GOMS analysis techniques that differ in
appearance and form, underlying architectural assumptions, and predictive
power. This article compares and contrasts four popular variants of the GOMS
family (the Keystroke-Level Model, the original GOMS formulation, NGOMSL, and
CPM-GOMS) by applying them to a single task example.

Network-accessible multimedia databases, repositories, and libraries are
proliferating at a rapid rate. A crucial problem for these repositories
remains timely and appropriate document access. In this article, we borrow a
model from psychological research on human memory, which has long studied
retrieval of memory items based on frequency and recency rates of past item
occurrences. Specifically, the model uses frequency and recency rates of prior
document accesses to predict future document requests. The model is
illustrated by analyzing the log file of document accesses to the Georgia
Institute of Technology World Wide Web (WWW) repository, a large multimedia
repository exhibiting high access rates. Results show that the model predicts
document access rates with a reliable degree of accuracy. We describe
extensions to the basic approach that combine the recency and frequency
analyses and which incorporate repository structure and document type. These
results have implications for the formulation of descriptive user models of
information access in large repositories. In addition, we sketch applications
in the areas of design of information systems and interfaces and their
document-caching algorithms.